Apparatus and method for ink jet recording

Abstract

The present invention provides an ink jet printer which performs recording by causing a nozzle to discharge an ink drop onto a recording medium. The nozzle is connected to an ink channel in which aqueous ink is housed. The printer head can vary the dot size on the recording medium by changing the size of the drop that is discharged from the nozzle. The aqueous ink has a degree of surface tension change ΔS that is expressed by the relation ΔS=(S 1 -S 3 )/ S 2 of 0.3 or less, wherein S 2 is the surface tension at 25° C., and has a value of 20 to 50 dynes/cm, S 1 is the surface tension at 5° C., and S 3 is the surface tension at 40° C.

What is claimed is: 
     
       1. An ink jet printer which performs recording by causing an ink drop to be discharged from a nozzle and allowing the ink drop to deposit on a recording medium, the ink jet printer comprising a printer head including a nozzle for discharging ink drops and an ink channel in which an aqueous ink is housed,   the printer head being capable of varying a dot size on the recording medium by changing the size of the ink drop to be discharged from the nozzle; and   the aqueous ink having a degree of surface tension change ΔS expressed by the relation ΔS=(S 1  -S 3 )/S 2  of 0.3 or less, and S 2  of 20 to 50 dyne/cm, in which S 2  is a surface tension of the aqueous ink at 5° C., S 2  is the surface tension at 25° C., and S 3  is the surface tension at 40° C.   
     
     
       2. An ink jet printer as set forth in claim 1, wherein the printer head includes a piezo-electric element such that by causing the piezoelectric element to be deformed, the volume of the ink channel is varied so that pressure is applied to the ink in the channel to cause ink to be discharged from the nozzle. 
     
     
       3. An ink jet printer as set forth in claim 2, wherein a quantity of volume change of the channel is varied depending on a quantity of deformation of the piezo-electric element to change a size of ink drop discharged from the nozzle. 
     
     
       4. An ink jet printer as set forth in claim 1, wherein the ΔS is 0.25 or less. 
     
     
       5. An ink jet printer as set forth in claim 4, wherein ΔS is 0.20 or less. 
     
     
       6. An ink jet printer as set forth in claim 1, wherein viscosity of the ink at 25° C. is 1.5 to 4.5 cps. 
     
     
       7. An ink jet printer as set forth in claim 1, wherein pH of the ink at 25° C. is 7 to 10. 
     
     
       8. An ink jet printer as set forth in claim 1, wherein the ink contains water, a color material, a water-soluble organic solvent, and a nonionic surface active agent. 
     
     
       9. An ink jet printer as set forth in claim 8, wherein the color material content of the ink is 0.5 to 20% by weight relative to the ink weight; the water-soluble organic solvent content is 1 to 30% by weight relative to the ink weight; and the nonionic surface active agent content is 0.01 to 5% by weight relative to the ink weight. 
     
     
       10. An ink jet printer as set forth in claim 9, wherein the water-soluble organic solvent contains at least one kind of alcohol solvents selected from the group consisting of glycerin, monoalkylene glycol, dialkylene glycol, trialkylene glycol, monoalkylene glycol lower alkyl ether, dialkylene glycol lower alkyl ether, trialkylene glycol lower alkyl ether, polyalkylene glycol having a molecular weight of 150 or more, and alkyl alcohol. 
     
     
       11. An ink jet printer as set forth in claim 9, wherein the nonionic surface active agent contains an alkylene oxide adduct of acetylene glycol. 
     
     
       12. An ink jet recording method in which multiple tone recording is performed by causing an ink drop to be discharged from a nozzle and allowing the ink drop to deposit on a recording medium, characterized in carrying out multiple tone recording on a recording medium by varying the size of ink drop discharged from a nozzle, the aqueous ink having a degree of surface tension change ΔS expressed by the relation ΔS=(S 1  -S 3 )/S 2  of 0.3 or less, and S 2  of 20 to 50 dyne/cm, in which S 1  is a surface tension of the aqueous ink at 5° C., S 2  is the surface tension at 25° C., and S 3  is the surface tension at 40° C. 
     
     
       13. An ink jet recording method as set forth in claim 12, wherein the ΔS is 0.25 or less. 
     
     
       14. An ink jet recording method as set forth in claim 13, wherein the ΔS is 0.20 or less. 
     
     
       15. An ink jet recording method as set forth in claim 12, wherein viscosity of the ink at 25° C. is 1.5 to 4.5 cps. 
     
     
       16. An ink jet recording method as set forth in claim 12, wherein pH of the ink at 25° C. is 7 to 10. 
     
     
       17. An ink jet recording method as set forth in claim 12, wherein the ink contains water, a color material, a water-soluble organic solvent, and a nonionic surface active agent. 
     
     
       18. An ink jet recording method as set forth in claim 17, wherein the color material content of the ink is 0.5 to 20% by weight relative to the ink weight; the water-soluble organic solvent content is 1 to 30% by weight relative to the ink weight; and the nonionic surface active agent content is 0.01 to 5% by weight relative to the ink weight. 
     
     
       19. An ink jet recording method as set forth in claim 18, wherein the water-soluble organic solvent contains at least one kind of alcohol solvents selected from the group consisting of glycerin, monoalkylene glycol, dialkylene glycol, trialkylene glycol, monoalkylene glycol lower alkyl ether, dialkylene glycol lower alkyl ether, trialkylene glycol lower alkyl ether, polyalkylene glycol having a molecular weight of 150 or more, and alkyl alcohol. 
     
     
       20. An ink jet recording method as set forth in claim 18, wherein the nonionic surface active agent contains an alkylene oxide adduct of acetylene glycol.